Re: [PATCH 2/9] KVM: x86: simplify read_emulated

Marcelo Tosatti
2012-07-20T00:49:30Z

On Tue, Jul 17, 2012 at 09:51:34PM +0800, Xiao Guangrong wrote:
> No need split mmio read region into 8-bits pieces since we do it in
> emulator_read_write_onepage
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> ---
> arch/x86/kvm/emulate.c | 29 ++++++++++++-----------------
> 1 files changed, 12 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 97d9a99..2d1916b 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -1166,24 +1166,19 @@ static int read_emulated(struct x86_emulate_ctxt *ctxt,
> int rc;
> struct read_cache *mc = &ctxt->mem_read;
>
> - while (size) {
> - int n = min(size, 8u);
> - size -= n;
> - if (mc->pos < mc->end)
> - goto read_cached;
> -
> - rc = ctxt->ops->read_emulated(ctxt, addr, mc->data + mc->end, n,
> - &ctxt->exception);
> - if (rc != X86EMUL_CONTINUE)
> - return rc;
> - mc->end += n;
> + if (mc->pos < mc->end)
> + goto read_cached;
>
> - read_cached:
> - memcpy(dest, mc->data + mc->pos, n);
> - mc->pos += n;
> - dest += n;
> - addr += n;
> - }
> + rc = ctxt->ops->read_emulated(ctxt, addr, mc->data + mc->end, size,
> + &ctxt->exception);
> + if (rc != X86EMUL_CONTINUE)
> + return rc;
> +
> + mc->end += size;
> +
> +read_cached:
> + memcpy(dest, mc->data + mc->pos, size);

What prevents read_emulated(size > 8) call, with
mc->pos == (mc->end - 8) now?

> + mc->pos += size;
> return X86EMUL_CONTINUE;
> }